1. Field of the Invention
This invention relates to heating and heat retaining work chamber structures, in particular, to covers and masonry with metallic supports therein.
2. Description of the Prior Art
The reason for using a pit cover over an open top carbon anode baking furnace is the same as for using a lid on a cooking pan-heat retention. Open top furnaces for baking carbon anodes immersed in fluid coke were designed some time ago when natural gas was cheap and plentiful. Now that this is no longer the case because prices are higher and supplies are not so plentiful, the inefficient utilization of energy for heating the furnaces has become an economic problem to be overcome.
One way to overcome this problem is to employ pit covers over the carbon anode baking furnaces which previously had open tops. Without pit covers, only four carbon anodes could be stacked in a row because the top carbon anode could not be too close to the surface of the fluid coke. If the top carbon anode was not immersed deeply enough in the fluid coke, it would not get sufficiently hot and, therefore, would not be baked properly for subsequent use as a good electrical conductor in reducing alumina to aluminum.
Pit covers per se are known and are exemplified by the unnumbered elements shown incidentally but not discussed in U.S. Pat. No. 4,131,417, issued to Donald D. Dwight on Dec. 26, 1978, and assigned to Aluminum Company of America, Pittsburgh, Pa.
The insulative properties of pit covers that are simply concrete slabs are minimal at best. Because the slabs are placed directly on top of the fluid coke, they do not effectively seal the surface of the furnace. Since the furnace is being run in a partial vacuum, outside room air is drawn into the furnace through the cracks left between the slabs and the walls near the top surface of the furnace. This outside room air cools the fluid coke and the top carbon anode. More fuel is, thus, unnecessarily wasted in heating the top carbon anode. A pit cover that would effectively seal the top surface of the furnace would reduce fuel consumption.
Efforts by others to make a suitable pit cover out of insulative castable refractory material which would effectively seal the furnace and reduce fuel consumption have met with failure. Thus, generally speaking, the carbon anode baking industry has turned away from the use of such materials and has attempted to solve the problems discussed above by other means. The failure of the industry and its search in other directions is discussed in U.S. Pat. No. 4,097,228, issued to Denys R. Rosling on June 27, 1978, and assigned to Babcock & Wilcox Co., New York, N.Y. This patent describes a flexible insulating blanket made of ceramic fiber and attached to a metal backing with adjustable panels thereon for sealing the open top of a carbon anode baking furnace. However, this type of pit cover is difficult to handle and time consuming to install. They are expensive to manufacture and the flexible insulating blanket made of ceramic fiber does not hold up in service.
Thus, it still remains a problem in the carbon anode baking industry to make a pit cover which will effectively seal the open top of the furnace and will significantly reduce fuel consumption.